I. Technical Field
The present invention relates to a shaft sealing device for shaft-sealing a fluid using a sealing member and, particularly, to a shaft sealing device using an electro stimuli-responsive macromolecular material and to a valve structure using the same.
II. Description of the Related Art
Generally, in the case of sealing a fluid in a container at all times, a shaft sealing device using a sealing member is utilized. The shaft sealing device is intended to seal the flow of the fluid via the sealing member. As the sealing member of the shaft sealing device, an annular O-ring or packing substantially circular in cross section, for example, is used in order to seal a wide variety of fluids including air, water, oil and gas. The sealing member is required to have high sealing performance because the principal function thereof is to seal the fluids.
For this reason, the sealing member is axially attached to a groove of a substantially rectangular shape in cross section formed within the same plane in the radial direction of a shaft or hole of one of members in the shaft sealing device and, when attaining a seal by pressure of contact with the other of the members in the shaft sealing device, is compressed by the shape of the groove. It is therefore required to have a compression allowance. After the assemblage of the shaft sealing device, the O-ring, for example, is compressed via the compression allowance to produce a repulsion force and, by the repulsion force, fulfills contact surface pressure sealability to attain a shaft seal.
In addition, the O-ring is generally made from one of various kinds of synthetic rubber materials. In order to fulfill an appropriate compression stress within a range in which extraordinary deformation is not induced, the material is required to have a prescribed low compression set and further satisfy characteristics including antiweatherability, abrasion resistance, heat resistance, cold resistance, oil resistance and chemical resistance. In addition, since O-rings are used in shaft sealing devices over a wide variety of fields including fields of automobiles, constructing machines, airplanes, office automation equipment and industrial instruments, for example, the material for the O-rings is selected to have an appropriate compression allowance in accordance with an intended field (purpose) and, even when being used in either a state accompanying the movement of a shaft sealing portion or a stationary state not accompanying the movement of the shaft sealing portion, fulfills durability, insertability and pressing crack prevention, not to mention securement of a shaft-sealing function. Thus, an ordinary shaft sealing device aims first at enhancing a sealing function with a sealing member, such as an O-ring. Generally, therefore, a sealing region of the sealing member or fluid is determined at a prescribed location. An apparatus having such a sealing device embedded therein has a complicated internal structure.
Assuming now that it is necessary to switch the sealing region to an unsealing region, a section of attachment of a sealing member or housing in the sealing region has to be provided with a separate moving mechanism in order to move the sealing region. The moving mechanism includes a screw feed mechanism, a piston-cylinder mechanism and a rotating mechanism, for example. In order to operate these mechanisms, it is necessary to use some power means, such as human power, electricity, air, hydraulic pressure, spring, etc.
On the other hand, not a sealing mechanism, but a valve using a so-called artificial muscle and having no complicated power means is disclosed (refer to Japanese Patent No. 3,501,216, for example). This valve uses an artificial muscle as a valving element and deforms the valving element per se to enable opening and closing a flow path. The valve disclosed in the Document uses as the valving element the artificial muscle formed of an electrostrictive elastic polymer film and deforms the valving element through a voltage ON-OFF operation to bring the valving element into contact with and separation from a valve seat, thereby opening and closing the flow path. The artificial muscle in this valve is called an EPAM (Electroactive Polymer Artificial Muscle) comprising a thin rubber-like macromolecular film (elastomer) and elastic electrodes sandwiching the film, in which voltage is applied between the electrodes to elongate the macromolecular film in a plane direction (to diameter-enlarge it in a circumferential direction).